A variety of absorbent structures, for example, sanitary napkins, panty liners and diaper liners for rubber pants, are constructed using pressure sensitive adhesives as positioning adhesives for attaching the article to the supporting garment.
There are a number of critical properties needed for these applications, specifically, the viscosity profile must be such that the adhesive will flow onto and partially penetrate the surface to which it is applied, yet allow a significant amount of the adhesive to remain on the exposed surface. Further, the adhesive coating must have good bond strength with high initial tack, yet the adhesive film must not transfer to the garment or cause pulling of the fibers or tearing of the garment when the absorbent article is removed.
Hot melt pressure sensitive adhesives are most commonly used for this positioning purpose with those disclosed in U.S. Pat. No. 4,136,699 being representative of the adhesives in current commercial use. In order to obtain the necessity properties, the compositions disclosed in U.S. Pat. No. 4,136,699 require the use of specific block copolymers wherein the mid-block is hydrogenated and wherein relatively large amounts of oil are needed in proportion to the amount of block copolymer. These hydrogenated copolymers are relatively expensive raw materials and are difficult to tackify.
It is an object of the present invention to prepare a hot melt pressure sensitive adhesive composition suitable for use as a positioning adhesive. More specifically, the adhesive compositions disclosed herein are prepared utilizing more economical, more easily tackifiable raw materials which unexpectedly produce stronger bonds than are found with the current commercial products with no adhesive transfer onto the undergarment.